JPH0430916A - Control method and device for wire-cut electric discharge machine - Google Patents

Abstract

PURPOSE:To prevent the breakage of a wire electrode by stopping pulse electrically discharging when each detected temperature of the wire electrode exceeds the first specified threshold temperature and restarting pulse electrically discharging when the detected temperature of the wire electrode becomes lower than the second specified threshold temperature. CONSTITUTION:The electric resistance of a wire electrode 10 is detected in the area opposing to a workpiece 12 and the wire electrode 10 at every quiescent time of pulse electric discharging, and the temperature of the wire electrode in the opposed area is detected from the detected value of the electric resistance, and the first specified threshold temperature and the second specified threshold temperature, which is lower than the first specified threshold temperature, are set to the detected temperature of the wire electrode beforehand. When each detected temperature of the wire electrode 10 exceeds the first specified threshold temperature, pulse electrically discharging is made to stop, and when the detected temperature of the wire electrode 10 becomes lower than the second specified threshold temperature, pulse electrically discharging is restarted. Owing to this constitution, the wire electrode 10 is prevented from breaking.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a control method and a control device for a wire electrical discharge machine, particularly in an electrical discharge machining area where a workpiece and a wire electrode face each other through a small gap. Considering that wire electrodes are prone to breakage when they reach an overheating state due to pulsed discharge current, the temperature of the wire electrode passing through the electrical discharge machining section is detected to prevent overheating, thereby preventing wire electrode breakage. The present invention relates to a control method and apparatus for controlling the supply of pulsed discharge power so as to achieve the following.

[Prior art]

Generally, in wire electrical discharge machining, a workpiece to be machined and a wire electrode to be traveled and fed are opposed to each other via a small gap, and pulsed discharge power is applied to both of them to generate a pulsed discharge through the small gap. A relative displacement in two-dimensional directions is applied between the workpiece and the wire electrode according to a desired machining shape, and the workpiece is machined using electrical discharge energy. For this purpose, a pulsed discharge current flows through the wire electrode, and the wire electrode is heated by Joule heat and the thermal effect of the discharge. At this time.

The wire electrode is constantly being cooled by the machining fluid, but especially in areas where the machining trajectory is complex, the balance between the cooling effect of the machining fluid and the heated state of the wire electrode caused by the generated heat is lost. Insufficient cooling may cause an overheating state in which the temperature of the wire electrode increases, and the mechanical strength of the wire electrode may decrease, leading to wire breakage.

[Problem to be solved by the invention]

However, conventionally, there has been a method of directly measuring or detecting whether or not the temperature of a wire electrode traveling through and passing through a wire electrical discharge machining section has reached a temperature state that easily causes wire breakage. A passive method is to maintain a balance between heat generation and the cooling effect of the machining fluid by keeping the current applied to the electrode and the machining fluid pressure constant with a safety factor in mind, thereby suppressing the rise in temperature of the wire electrode in the electrical discharge machining area. It had been taken.

In other words, since it is necessary to set the machining conditions in wire electric discharge machining in advance to the safe side, it is necessary to set the machining speed to the low speed side, which is slower than the desired speed value, or to set the pulse discharge power to the low output side. He was taking a passive approach. In this case, there were problems such as a decrease in wire electrical discharge machining efficiency. Therefore, the present invention directly detects the temperature state of the wire electrode passing through the electrical discharge machining area, compares the same temperature with a reference temperature to monitor the wire electrode breakage limit, and gradually detects the wire electrode before the breakage occurs. Therefore, it is an object of the present invention to provide a control method and a control device for a wire electric discharge machine that can reduce pulse discharge power, which is a factor that causes the temperature of the wire electrode.

[Means to solve the problem]

The present invention calculates the electric resistance value of a wire electrode that is fed in the axial direction and passes through the electric discharge machining area including the upper and lower areas centered on the discharge gap area where the workpiece and the wire electrode face each other when the workpiece and the wire electrode are facing each other. By measuring the temperature every hour, calculating and detecting the temperature state of the wire electrode from the same electrical resistance value, and comparing the detected temperature value with a predetermined threshold temperature, it was found that the wire electrode had reached an overheated state. In this method, the above problem is solved by suppressing the occurrence of pulse discharge by gradually expanding the pause width of the discharge pulse, and restarting the pulse discharge when the temperature of the wire electrode decreases. be.

That is, according to the present invention, a wire electrical discharge machining is performed in which a pulse discharge is generated through a micro gear knob in which a workpiece to be machined and a wire electrode face each other, and at the same time, the workpiece and the wire electrode are relatively displaced in a two-dimensional direction to perform electrical discharge machining. In the control method of the machine, the electrical resistance of the wire electrode is detected in the opposing area between the workpiece and the wire electrode every time the pulse discharge is stopped, and the temperature of the wire electrode in the opposing area is determined based on each detected value of the electrical resistance. and setting in advance a first predetermined threshold temperature and a second predetermined threshold temperature lower than the first predetermined threshold temperature for the detected temperature of the wire electrode, and each of the wire electrodes When the detected temperature exceeds the first predetermined threshold temperature, the pulse discharge is stopped, and the pulse discharge is continued to be stopped until the detected temperature value of the wire electrode falls below the second predetermined threshold temperature. ,
A control method for a wire electric discharge machine is provided, in which the noflus discharge is restarted when the detected temperature value of the wire electrode falls below the second predetermined threshold temperature.

Further, according to the present invention, a wire is used to perform electrical discharge machining by performing Norms discharge through a minute gap where a workpiece to be machined and a wire electrode face each other, and at the same time displacing the workpiece and the wire electrode relative to each other in a two-dimensional direction. A control device for an electrical discharge machine, comprising: a pulse generating means for applying pulsed power to generate a pulsed discharge in a minute gap between the workpiece and the wire electrode via a feeder in contact with the wire electrode; and a pulse generated by the pulse generating means. resistance detection means for contactingly detecting the electrical resistance value of the wire electrode located in the area facing the workpiece every time the discharge is paused; and the wire located in the facing area based on the electrical resistance value detected by the resistance detection means. temperature detection means for calculating and detecting the temperature of the electrode; and when the wire electrode temperature detected by the temperature detection means exceeds a first predetermined threshold temperature, the pulse generation means stops applying pulse power, The application of the pulsed power is continued until the detected value of the electrode temperature falls below a second predetermined threshold temperature that is lower than the first predetermined threshold temperature, and the detected temperature value of the wire electrode becomes the second predetermined threshold temperature. A control device for a wire electric discharge machine is provided, which includes a discharge control means for restarting pulse discharge when the discharge has decreased further.

Hereinafter, the present invention will be explained in more detail based on embodiments shown in the accompanying drawings.

〔Example〕

FIG. 1 is a block diagram mechanically illustrating a control device for implementing a control method in wire electrical discharge machining according to the present invention;
FIGS. 2(a) to 2(d) are graphs showing waveforms and timing, and FIG. 3 is a flowchart illustrating the determination operation by which the control unit determines the temperature state of the wire electrode.

In FIG. 1, a wire electrode 10 of a wire electric discharge machine is connected to a workpiece 12 via a discharge gap from a wire electrode supply source consisting of a wire electrode supply bobbin through a plurality of guide rollers and tension rollers, as is well known. It passes through the opposing electrical discharge machining area shown in the figure while running under a constant tension, and is collected by a collection roller or a collection box. At this time, the Σ-ri 12 is placed on the work table 14, and
As the work table 14 is fed through the servo mechanism 16 and controlled by figure value control, the work 12 is moved and displaced in two dimensions relative to the wire electrode 10, so that there is no space between the wire electrodes 10J. When a pulse discharge I6 is generated through the discharge gap, a wire discharge crab action is applied according to the desired machining shape. The above-mentioned pulse discharge is carried out from the first pulse generation stage 18 provided in the power supply section of the wire electric discharge machine to the diode D and a pair of contact type feeders 21.
a and 21b to the wire electrode 10, and the workpiece 12
Pulse discharge power is supplied to the wire electrode 10 and the workpiece 12 so that an electrical connection is made through the discharge gap. are arranged above and below the facing area of the pulse B so that sufficient pulse B electric power is supplied. The servo mechanism 16 and the pulse generating means 18 are both controlled by a control section 20 via an interface 19. This control unit 20 has arithmetic control means such as a microprocessor and memory means,
It is a device that performs wire electrical discharge machining under optimal machining conditions according to control data stored in advance in a machine program or memory means by inputting external commands from an NC tape, etc., and has traditionally been provided as the central part of wire electrical discharge machines. is well known.

Now, in addition to the above-described configuration, the present invention connects the constant current source 22 to the above-mentioned feeders 21a and 21b via the first switch 24 consisting of a semiconductor switch, and performs electrical discharge processing when the first switch 24 is turned on. A configuration is provided to supply a constant current to the wire electrode 10 passing through the area, and further, by contacting the wire electrode 10 passing through the electrical discharge machining area, the current flowing through the wire electrode 10 and the electrical resistance of the wire are reduced. Contacts 26a, 26b that take out the voltage value that is the product, a second switch 28 that is connected to the first switch 24 and operates on and off almost simultaneously, and contacts 26a, 26b when the second varnish inch 28 is turned on. It is equipped with a wire voltage detector 30 that detects the voltage value extracted from the voltage, an amplifier 32 that amplifies the detected voltage, and the like. The detected voltage amplified by the amplifier 32 is sent to the control unit 20 via the interface 19 after being appropriately A/D converted.

The operation of the above configuration will now be explained.

In the electrical discharge machining process in which the wire electrical discharge machine performs wire electrical discharge machining under the control of the control unit 20, the pulse generating means 18
Pulse discharge is performed between the work 12 and the work 12 by the pulse discharge power supplied from the work table 14. At the same time, the work 12 and the work table 14 undergo relative feeding displacement in the two-dimensional direction. Processing is carried out. The graph of FIG. 2(A) shows the pulses flowing through the wire electrode 10 when a discharge pulse is generated between the wire electrode 10 and the workpiece 12 by the pulse discharge power supplied from the pulse generating means 18. It shows the waveform of discharge current. At this time, the first switch 24 is switched from the control unit 20 via the interface 19 and the pulse generator 18 to the pulse discharge pause time τOFF.
A command to turn it on is issued over the period of time, and the first switch 24 is turned on every time there is a pause in pulse discharge, as shown in (b) of FIG. Further, after the first switch 24 is turned on for a predetermined period of time t, the second switch 28 is also turned on for approximately the same period of time, as shown in the graph of FIG. 2 (c).

As described above, the first switch 24 is turned on, that is, the pulse discharge pause time τ. A constant current is supplied from a constant current source 22 to the wire electrode 10 in the electrical discharge machining area every time FF is performed. This constant current is applied to the feeders 21a, 21b, the wire electrode 1
0, and at this time, the second switch 2
8 turns on after a delay time of 1r, the wire electrode 1o
Wire voltage detector 30 via contactor 26a126b
measures the voltage value of the wire electrode 1o in the electrical discharge machining area where a predetermined current flows. That is, the wire voltage detector 3o detects the voltage of the wire electrode 10 as the product of the constant current and the electrical resistance value of the wire electrode 1o. Therefore, when this detected voltage is amplified via the amplifier 32 and fed back to the control unit 2Q via the interface I9 after A/D conversion,
The electrical resistance value Rt of the wire electrode 10 is calculated and detected from this detected voltage.

This electrical resistance value Rt is the wire electrode 10 in the electrical discharge machining area.
The temperature value of the wire electrode 10 when measuring the voltage of the wire electrode 10 can be calculated and detected from the following well-known formula.

Rt ” Rt. [1+α (t to)] ”'■
Here, Rt is the electrical resistance value of the wire electrode 10 at a temperature t, and Rto is the temperature t of the wire electrode 10. , for example, a constant normal temperature value 1. The electrical resistance value α of the wire electrode 10 in is a temperature coefficient determined depending on the material of the wire electrode 10 and is well known.

In this way, the control unit 20 directly detects the temperature of the wire electrode 10 in the electrical discharge machining area. The graph of (d) in FIG. 2 shows the actual temperature value of the wire electrode ICI obtained by further calculating according to the above formula 0 from the directly measured values and calculated values of the voltage and electrical resistance of the wire electrode 10. It shows.

At this time, the temperature of the wire electrode 10 increases and decreases due to the Joule heat caused by the pulsed discharge current and the thermal effect associated with the discharge due to the electrical discharge machining action. It is directly detected through changes in the electrical constants of .

Therefore, the control unit 20 experimentally determines the temperature state at which wire breakage occurs according to the physical characteristics and material characteristics of the wire electrode 10, and determines the first threshold temperature TA and the first threshold temperature T.
The current wire electrode 10 is determined based on the second threshold temperature T3 which is lower than A and is in a safe area where there is no risk of wire breakage.
The wire electrical discharge machining is continued by continuing the pulse discharge in the electrical discharge machining area as usual in the range where the temperature does not exceed the first threshold temperature TA. On the other hand, when the current detected temperature exceeds the first threshold temperature TA, the pulse generating means 18 immediately stops supplying the pulse discharge power. The stop of this pulse discharge power actually occurs in the pulse discharge generation circuit when the pulse is stopped. A control method is adopted to increase the FF period, and the pulse discharge is stopped until the actual detected temperature of the wire electrode 10, that is, the current temperature, falls below the second threshold temperature TB. Let them do it. The phenomenon in the graph (d) of Figure 2 is -
Once the detected temperature of the wire electrode 10 exceeded the first threshold temperature Tk, the pulse discharge indicated by the dotted line in the graph of FIG. This shows that the pulse discharge was restored when the threshold temperature T of 2 was lowered.

As described above, the present invention directly detects the temperature state of the wire electrode 10 passing through the discharge area facing the workpiece 12 through measurement and calculation of electrical constants during the progress of the wire electric discharge machining process. The temperature is compared and determined with a reference temperature value, and control is performed to prevent the wire electrode 10 from breaking.

FIG. 3 shows that the control unit 20 compares and discriminates the above-mentioned first and second threshold temperatures TA and TB stored in its built-in memory means, and controls the continuation or stop of the pulse discharge as described above. This is a flowchart showing the operation process, in which the comparison and discrimination operations are of course performed by arithmetic control means such as a microprocessor, and the operation of the pulse generation means 18 is controlled via the interface 19 according to the discrimination results. be. Note that the above first and second threshold temperatures TA
, TB can be freely set by the control unit 20 from an external contact means according to the material characteristics and physical characteristics of the wire electrode 10 used.

σEffects of the Invention] As is clear from the above description of the present invention, according to the present invention, the electric discharge machining area including the upper and lower areas centered on the discharge gap area where the workpiece to be machined and the wire electrode face each other is fed. The electrical constants such as the voltage and electrical resistance of the wire electrode passing under the running force are measured at each pause time of pulse discharge, and the actual temperature state of the wire electrode is directly calculated and detected from the electrical constants. By comparing the detected current wire temperature value with a predetermined threshold temperature, when it is found that the wire electrode has reached an overheating condition, the pause width τ of the discharge pulse is gradually reduced. The pulse width τ of the pulse discharge can be increased by expanding the FF. , to virtually zero to suppress the occurrence of electrical discharge, and when it is confirmed that the temperature of the wire electrode has fallen below the threshold, the pulsed electrical discharge is resumed.This allows for online control while the wire electrical discharge machining process continues. This makes it possible to prevent the wire electrode from breaking, and as a result, it becomes possible to significantly improve the machining efficiency of wire electrical discharge machining.

[Brief explanation of the drawing]

FIG. 1 is a block diagram mechanically illustrating a control device for implementing a control method in wire electrical discharge machining according to the present invention;
FIGS. 2(A) to 2(D) are graphs showing waveforms and timing, and FIG. 3 is a flowchart explaining the determination operation by which the control unit determines the temperature state of the wire electrode. 10...Wire electrode, 12...Work, 18
... Pulse generating means, 20 ... Control section, 21a, 2
1b=・Feeder, 22... Constant current source, 24... First switch,
26a, 26b - Contactor, 28... Second switch, 30... Wire voltage detector.

Claims (1)

[Scope of Claims] 1. Wire electrical discharge machining in which electrical discharge machining is performed by performing pulse electrical discharge through a minute gap in which a workpiece to be machined and a wire electrode face each other, and at the same time displacing the workpiece and wire electrode relative to each other in a two-dimensional direction. In the control method of the machine, the electrical resistance of the wire electrode is detected in the opposing region between the workpiece and the wire electrode every time the pulse discharge is stopped, and the temperature of the wire electrode in the opposing region is determined from each detected value of the electrical resistance. , a first predetermined threshold temperature and a second predetermined threshold temperature lower than the first predetermined threshold temperature are set in advance for the detection temperature of the wire electrode, and each detection of the wire electrode When the temperature exceeds the first predetermined threshold temperature, the pulse discharge is stopped; the pulse discharge is continued to be stopped until the detected temperature value of the wire electrode falls below the second predetermined threshold temperature; A method for controlling a wire electric discharge machine, characterized in that pulse discharge is restarted when a detected temperature value of the wire electrode falls below the second predetermined threshold temperature. 2. In a control device for a wire electric discharge machine that performs electric discharge machining by performing pulse discharge through a minute gap where a workpiece to be machined and a wire electrode face each other, and at the same time displacing the workpiece and the wire electrode relative to each other in a two-dimensional direction, pulse generating means for applying pulsed power to generate a pulse discharge in a minute gap between the workpiece and the wire electrode via a feeder contacting the wire electrode; resistance detection means for contactingly detecting the electrical resistance value of the wire electrode in the opposing region; and a temperature for calculating and detecting the temperature of the wire electrode in the opposing region from the electrical resistance value detected by the resistance detection means. detecting means; when the wire electrode temperature detected by the temperature detecting means exceeds a first predetermined threshold temperature, the application of pulsed power by the pulse generating means is stopped, and the detected value of the wire electrode temperature is set to The application of the pulsed power is continued until the temperature drops below a second predetermined threshold temperature, which is lower than the second predetermined threshold temperature, and the pulsed discharge is restarted when the detected temperature value of the wire electrode falls below the second predetermined threshold temperature. 1. A control device for a wire electrical discharge machine, comprising: electrical discharge control means. 3. The resistance detection means for detecting the electrical resistance of the wire electrode in the area facing the workpiece is configured to connect a constant current power source, and one of the pulse generating means and the constant current power source to the area facing the workpiece. a first switch means electrically connected to the feeder in contact with a certain wire electrode, and the first switch means is in an area facing the workpiece when the constant current power source is connected to the feeder. a second switch means for connecting a wire electrode to a voltage detection circuit via an electric contact; a voltage value of the wire electrode in the opposing area detected by the voltage detection circuit; and a constant current supplied from the constant current source. 3. The control device for a wire electrical discharge machine according to claim 2, further comprising an electrical resistance calculation means for calculating the electrical resistance value from the electrical resistance value.